1. Field of the Invention
The present invention relates primarily to an apparatus and method for repairing pipes and conduits, particularly relatively high-pressure pipes and conduits, such as a watermain. More particularly, the invention is directed to an internal repair of a section of damaged, weakened, or leaking pipe or conduit, in which the section to be repaired is typically located in an inaccessible area, such as underground. Although conduit repair is an intended specific application of the invention, the apparatus and method disclosed has broader applicability and are contemplated to encompass the securing of a curable sealant to a surface and the general bonding of two surfaces together.
2. Description of Background and Relevant Information
Conduit systems for conveying water are typically located underground and, in general, are not easily accessible if repair or other maintenance is required after installation. Over a period of time, such conduit systems can become damaged, weakened, or can otherwise begin to leak, particularly at the joints between adjacent conduit sections, but also longitudinally along a conduit section.
Problems associated with such systems, and a number of previous repair methods and apparatuses are disclosed, for example, in U.S. Pat. Nos. 5,119,862 and 5,351,720. These patents, which disclose "No-Dig" or non-excavation repairs, utilize a sleeve or liner which is transported to the site of the weakened or damaged pipe in a coiled or partially coiled configuration. Once the repair liner is located in the necessary position at the site of the repair, internal pressure is applied to the sleeve by means of an inflatable bladder or other means, which causes the sleeve to begin to uncoil and expand in the direction of the "host" pipe to be repaired. The sleeve, which includes a gasket or sealing compound on its outer surface, reaches a slight over-expanded condition, whereby the liner compresses the gasket or sealing compound against the inner surface of the host pipe. The internal pressure is then reduced or removed and the sleeve is slightly recoiled, whereby overlapping edges of the sleeve become locked in place by virtue of complementary locking means.
The methods and apparatus disclosed in the aforementioned patents are intended primarily for the repair of conduits that carry wastewater and other fluids that are not in an over-pressure environment. However, a high-pressure pipe, such as a watermain, also requires periodic repair, particularly for sealing against ex-filtration, i.e., against a leak of liquid from the inside to the outside of the pipe. In addition, old leaded joints must be isolated to prevent the leaching of lead into drinking water.
The methods and apparatus disclosed in the aforementioned patents are useful for the repair of high-pressure pipes, although a particular problem, explained below, is posed. Reference will be made to FIGS. 1A, 1B, and 1C in explaining this problem. FIGS. 1A-1C are similar to FIGS. 3A-3C of U.S. Pat. No. 5,119,862, but illustrate the problem created when a sealant suitable for over-pressure pipe repair is used. The size of these pipes is typically between 4 inches and 36 inches in diameter or even greater.
Unlike an elastic compressible gasket or a polyurethane foam, e.g., which are usable for the repairs described in U.S. Pat. No. 5,351,720, high-pressure or over-pressure pipes and conduits require sealants that cure into a concrete-like hardness and which are not compressible. Such resins, unlike compressible or foam sealants, do not expand as they cure. Instead, they more or less retain their initial liquid volume. Although epoxy sealants are contemplated, polyester sealants, for example, are contemplated for conduits that convey potable water.
FIG. 1A schematically illustrates a portion of a coiled repair sleeve 10, which is coiled within a damaged or leaking host pipe 11 prior to or shortly after internal expansion or uncoiling of the repair sleeve has begun, by means of apparatus known in the art, such as an inflatable air bag. The outer surface of the sleeve carries a layer of curable resin 12, such as an epoxy or epoxy-like resin. One edge of the sleeve 10 constitutes a male locking member 13 which is to be inserted into the female member 14 formed at an opposite edge of the sleeve to thereby lock the sleeve in place to effect the necessary repair.
As the air bag or other internal expansion means continues to uncoil the sleeve 10, the sleeve exerts pressure against the inside of the host pipe 11 and squeezes the resin 12 between the sleeve and the host pipe, as shown in FIG. 1B. In addition, the male locking member 13 slides over the internal lower lip 15 of the female locking member 14 until the male locking member is forced beyond the end of the lower lip 15.
As the air bag is then deflated, or other internal expansion means is de-activated, the sleeve 10 coils, due to its spring-like property, or due to the use of a compressible gasket or due to the back pressure of limit straps placed around the coil prior to expansion thereof, so that the male locking member 13 forces itself into the female locking member 14, above the lower lip 15, so that the sleeve assumes its locked position. This locked position is shown in FIG. 1C.
After the layer of resin cures and hardens, however, a gap G is created since the layer of resin tends to retain its previous thickness conferred by the over-expanded condition in FIG. 1B.
Following the repair, when water or fluid pressure is then applied within the host pipe 11, the air gap G prevents resistance to expansion of the sleeve 10. Damage or unlocking of the sleeve can possibly result.